1. Field of the Invention
The present invention relates to a capacitor element, a laminated thin-film device using a capacitor element, and a circuit using a capacitor element. More particularly, the present invention relates to a capacitor element that has, in the dielectric layer, a well region for shifting or shifting and expanding a capacitance-voltage curve (called, hereafter, as C-V curve) between electrode layers in at least one direction of the plus direction and the minus direction with respect to the voltage axis, a laminated thin-film device using the capacitor element, and a circuit using the capacitor element.
2. Description of the Related Art
Integrated thin-film capacitors that use perovskite materials with a high relative dielectric constant are used for various applications, such as a storage node capacitor of a dynamic RAM (DRAM), a decoupling capacitor, a voltage tunable capacitor in a high frequency region (RF), a microwave filter, a phase shifting element in a phased array antenna, and a pyroelectric sensor, and are therefore being energetically researched at the moment.
The capacitance of the dielectric layer is given by C=∈∈0A/d (wherein C is the dielectric constant of the dielectric layer, .epsilon. is the relative dielectric constant of the dielectric layer, ∈0 is the dielectric constant of the vacuum, A is a cross-sectional area of an electrode, and d is the distance between electrode layers), and since .epsilon. depends on the voltage applied between the electrode layers, C also changes depending on the voltage. The capacitance dependency on voltage of the perovskite material with a high dielectric constant in a thin film can be described clearly by the Landau Ginsberg Devonshire (LGD) theory.
Because of such a capacitance dependency on voltage, the capacitance dependency on voltage has an extremely important meaning in an integrated thin-film capacitor.
There are some dielectrics that have a low capacitance dependency on voltage, but such dielectrics normally have a low dielectric constant. Therefore for a capacitor element for laminated thin-film devices that have a high necessity to use a dielectric layer with a high dielectric constant, the capacitance dependency on voltage has an especially significant meaning.
In the case of a storage node capacitor of a DRAM, decoupling capacitor, etc., for example, it is desirable that the capacitance dependency on voltage should be as low as possible. In the case of a voltage tunable capacitor, on the other hand, it is desirable to optimize the capacitance dependency on voltage.
Because of such a reason, a laminated thin-film device wherein the capacitance dependency on voltage can be appropriately adjusted is desired.
However, an effective means has not been available, except by selecting the material to be used, such as for the dielectric layer.